Spin Hamiltonian Parameters for Cu(II)−Prion Peptide Complexes from L-Band Electron Paramagnetic Resonance Spectroscopy

Cu(II) is an essential element for life but is also associated with numerous and serious medical conditions, particularly neurodegeneration. Structural modeling of crystallization-resistant biological Cu(II) species relies on detailed spectroscopic analysis. Electron paramagnetic resonance (EPR) can, in principle, provide spin Hamiltonian parameters that contain information on the geometry and ligand atom complement of Cu(II). Unfortunately, EPR spectra of Cu(II) recorded at the traditional X-band frequency are complicated by (i) strains in the region of the spectrum corresponding to the g∥ orientation and (ii) potentially very many overlapping transitions in the g⊥ region. The rapid progress of density functional theory computation as a means to correlate EPR and structure, and the increasing need to study Cu(II) associated with biomolecules in more biologically and biomedically relevant environments such as cells and tissue, have spurred the development of a technique for the extraction of a more complete set of spin Hamiltonian parameters that is relatively straightforward and widely applicable. EPR at L-band (1−2 GHz) provides much enhanced spectral resolution and straightforward analysis via computer simulation methods. Herein, the anisotropic spin Hamiltonian parameters and the nitrogen coordination numbers for two hitherto incompletely characterized Cu(II)-bound species of a prion peptide complex are determined by analysis of their L-band EPR spectra

Quantum chemical study of the effect of precursor stereochemistry on dissociative chemisorption and surface redox reactions during the atomic layer deposition of the transition metal copper

Using quantum chemical calculations, we investigate surface reactions of copper precursors and diethylzinc as the reducing agent for effective Atomic Layer Deposition (ALD) of Cu. The adsorption of various commonly used Cu(II) precursors is explored. The precursors vary in the electronegativity and conjugation of the ligands and flexibility of the whole molecule. Our study shows that the overall stereochemistry of the precursor governs the adsorption onto its surface. Formation of different Cu(II)/Cu(I)/Cu(0) intermediate complexes from the respective Cu(II) compounds on the surface is also explored. The surface model is a (111) facet of a Cu55 cluster. Cu(I) compounds are found to cover the surface after the precursor pulse, irrespective of the precursor chosen. We provide new information about the surface chemistry of Cu(II) versus Cu(I) compounds. A pair of CuEt intermediates or the dimer Cu2Et2 reacts in order to deposit a new Cu atom and release gaseous butane. In this reaction, two electrons from the Et anions are donated to copper for reduction to metallic form. This indicates that a ligand exchange between the Cu and Zn is important for the success of this transmetalation reaction. The effect of the ligands in the precursor on the electron density before and after adsorption onto the surface has also been computed through population analysis. In the Cu(I) intermediate, charge is delocalized between the Cu precursor and the bare copper surface, indicating metallic bonding as the precursor densifies to the surface

Investigation of synthesis and some properties of the copper complexes containing imidazole ligand

The copper(II) complexes bearing tetrasubstituted imidazole derivatives containing oxygen donor as ligands (L1-6) were synthesized and characterized by spectroscopic methods, magnetic measurements, elemental and thermogravimetric analyses. The fluorescence efficiency of the ligands (L1-6) and their copper(II) complexes were investigated at r.t. in DMF solution. Theoretical calculations were performed for the copper(II) complex of L4 ligand, in this study. The molecular geometry, bond lengths, bond angles and vibrational wave numbers were calculated by using ab initio calculations based on the Hartree-Fock{HF/6-31G(d)} and the density functional theory {B3LYP/6-31G(d)} in the ground state

Mechanism for the atomic layer deposition of copper using diethylzinc as the reducing agent – a density functional theory study using gas phase molecules as a model

We present theoretical studies based on first-principles density functional theory calculations for the possible gas-phase mechanism of the atomic layer deposition (ALD) of copper by transmetalation from common precursors such as Cu(acac)(2), Cu(hfac)(2), Cu(PyrIm(R))(2) with R = (i)Pr and Et, Cu(dmap)(2), and CuCl(2) where diethylzinc acts as the reducing agent. An effect on the geometry and reactivity of the precursors due to differences in electronegativity, steric hindrance, and conjugation present in the ligands was observed. Three reaction types, namely, disproportionation, ligand exchange, and reductive elimination, were considered that together comprise the mechanism for the formation of copper in its metallic state starting from the precursors. A parallel pathway for the formation of zinc in its metallic form was also considered. The model Cu(I) molecule Cu(2)L(2) was studied, as Cu(I) intermediates at the surface play an important role in copper deposition. Through our study, we found that accumulation of an LZnEt intermediate results in zinc contamination by the formation of either Zn(2)L(2) or metallic zinc. Ligand exchange between Cu(II) and Zn(II) should proceed through a Cu(I) intermediate, as otherwise, it would lead to a stable copper molecule rather than copper metal. Volatile ZnL(2) favors the ALD reaction, as it carries the reaction forward

Synthesis, X-ray crystal structures, electrochemistry and theoretical investigation of a tetradentate nickel and copper Schiff base complexes

International audienceNew tetradentate mononuclear nickel(II) [NiL] and pentadentate binuclear copper(II) [Cu 2 L 2 H 2 O], H 2 O Schiff base complexes have been synthesized. The crystal structures of [NiL] and [Cu 2 L 2 H 2 O], H 2 O have been determined by X-ray diffraction method showing distorted square-planar geometry for [NiL] and distorted tetragonal pyramid geometry for [Cu 2 L 2 H 2 O], H 2 O. In both complexes, the dehydroacetic acid functional group engages in a deprotonated manner and coordination occurs through the nitrogen atoms of the imine function and the phenolic oxygen. Density Functional Theory calculations are carried out for the determination of the optimized structures. The fundamental vibrational wave numbers are calculated and a good agreement between observed and calculated wave numbers is achieved

Computational studies on heterogenization of homogeneous catalyst of iron(III), nickel(II) and copper(II) N,N′-disalicylidene-1,2-phenylenediamine complex

Density functional theory (DFT) calculations were carried out on iron(III), nickel(II) and copper(II) complexes of N,N′-ethylenebis(salicylimine) both at molecular level (isolated complexes) and encapsulated in a zeolite framework to investigate changes that occur in their geometrical and electronic parameters as well as in their reactivity and stability. The computational results showed that the zeolite encapsulated metal complexes have higher reactivity and less stability as compared to the isolated metal complexes.               KEY WORDS: Density functional theory, N,N′-ethylenebis(salicylimine), Computational studies, Heterogenization, Electronic parameters Bull. Chem. Soc. Ethiop. 2019, 33(1), 91-102DOI: https://dx.doi.org/10.4314/bcse.v33i1.

Synthetic, Crystallographic, and Computational Study of Copper(II) Complexes of Ethylenediaminetetracarboxylate Ligands

Copper(II) complexes of hexadentate ethylenediaminetetracarboxylic acid type ligands H4eda3p and H4eddadp (H4eda3p = ethylenediamine-N-acetic-N,N′,N′-tri-3-propionic acid; H4eddadp = ethylenediamine-N,N′-diacetic-N,N′-di-3-propionic acid) have been prepared. An octahedral trans(O6) geometry (two propionate ligands coordinated in axial positions) has been established crystallographically for the Ba[Cu(eda3p)]·8H2O compound, while Ba[Cu(eddadp)]·8H2O is proposed to adopt a trans(O5) geometry (two axial acetates) on the basis of density functional theory calculations and comparisons of IR and UV−vis spectral data. Experimental and computed structural data correlating similar copper(II) chelate complexes have been used to better understand the isomerism and departure from regular octahedral geometry within the series. The in-plane O−Cu−N chelate angles show the smallest deviation from the ideal octahedral value of 90°, and hence the lowest strain, for the eddadp complex with two equatorial β-propionate rings. A linear dependence between tetragonality and the number of five-membered rings has been established. A natural bonding orbital analysis of the series of complexes is also presented.

Re-evaluating the Cu K pre-edge XAS transition in complexes with covalent metal–ligand interactions

Three [Me2NN]Cu(h2 -L2) complexes (Me2NN ¼ HC[C(Me)NAr]2; L2 ¼ PhNO (2), ArF 2N2 (3), PhCH]CH2 (4); Ar ¼ 2,6-Me2-C6H3; ArF ¼ 3,5-(CF3)2-C6H3) have been studied by Cu K-edge X-ray absorption spectroscopy, as well as single- and multi-reference computational methods (DFT, TD-DFT, CASSCF, MRCI, and OVB). The study was extended to a range of both known and theoretical compounds bearing 2p-element donors as a means of deriving a consistent view of how the pre-edge transition energy responds in systems with significant ground state covalency. The ground state electronic structures of many of the compounds under investigation were found to be strongly influenced by correlation effects, resulting in ground state descriptions with majority contributions from a configuration comprised of a Cu(II) metal center anti-ferromagentically coupled to radical anion O2, PhNO, and ArF 2N2 ligands. In contrast, the styrene complex 4, which displays a Cu K pre-edge transition despite its formal d10 electron configuration, exhibits what can best be described as a Cu(I):(styrene)0 ground state with strong pbackbonding. The Cu K pre-edge features for these complexes increase in energy from 1 to 4, a trend that was tracked to the percent Cu(II)-character in the ground state. The unexpected shift to higher preedge transition energies with decreasing charge on copper (QCu) contributed to an assignment of the pre-edge features for these species as arising from metal-to-ligand charge transfer instead of the traditional Cu1s / Cu3d designation

An EPR investigation of binding environments by N-donor chelating exchange resins for Cu extraction from aqueous media

EPR and UV−vis spectroscopy were collectively used to characterize a series of Cu(II) binding environments within two chelating exchange resins, Dowex and CuWRAM, used for Cu(II) extraction from aqueous media. A series of well-defined intra- and intermolecular binding sites have been identified as responsible for Cu(II) uptake